This section is intended to provide a background or context to the disclosed embodiments. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), 3GPP Long Term Evolution (LTE), and orthogonal frequency division multiple access (OFDMA).
In a mobile wireless communication system, uplink (mobile station to base station) transmitter power control balances the need for sufficient energy transmitted per bit to achieve a desired quality-of-service (e.g., data rate and error rate), against the need to minimize interference to other users of the system and to maximize the battery life of the mobile terminal. To accomplish this goal, uplink power control has to adapt to the characteristics of the radio propagation channel, including path loss, shadowing, fast fading and interference from other users in the same cell and adjacent cells.
In LTE Rel-8, control signaling from a mobile station to a base station is carried on a physical uplink control channel (PUCCH) on a single carrier FDMA (frequency division multiple access) waveform. Control signaling includes scheduling requests (SR) for uplink transmissions, HARQ acknowledgments (ACK/NAK) for downlink data packets, channel quality indicators (CQI) and other information such as rank indicator (RI) and precoding matrix indicator (PMI) for downlink transmissions that indicate the modulation and coding scheme (MCS) that can be supported by the channel, taking into account the signal to noise plus interference ratio of the channel and the characteristics of the mobile station's receiver.
The control signaling on the PUCCH is transmitted in a frequency region on the edges of the system bandwidth. Each PUCCH transmission in one transmission subframe consists of one or more resource blocks (RB) at or near one edge of the system bandwidth in the first (0.5 millisecond) slot of the subframe, followed in the second (0.5 millisecond) slot of the subframe by a second set of resource blocks at or near the opposite edge of the system bandwidth.
LTE Rel-8 defines different PUCCH formats that carry different types and amounts of information including SR only, 1-bit and 2-bit HARQ ACK/NAK (corresponding to 1 codeword and 2 codeword transmissions), 11-bit CQI and 11-bit CQI with 1-bit and 2-bit HARQ ACK/NAK. The PUCCH power control algorithms in Rel-8 adjust power in proportion to the total number of HARQ bits and CQI bits, but the algorithms ignore the relative importance of HARQ bits and CQI bits and the 2 HARQ bits are inherently outweighed by the 11 CQI bits. The acceptable error rates for decoding HARQ ACK/NAK bits may be much lower than the acceptable error rate for decoding CQI bits, the reason being that a HARQ ACK/NAK decoding error (either a false positive or a false negative) may result in the acceptance of erroneous data or the rejection of accurate data.
Carrier aggregation (CA) has been proposed for LTE Advanced to aggregate two or more component carriers (CCs) per UE (e.g., up to five component carriers) to support wider transmission bandwidths for greater throughput. The PUCCH formats defined for LTE Rel-8 are inadequate to account for the number of HARQ ACK/NAK bits required for multiple component carriers (e.g., 5 carriers times 2 HARQ bits requires 10 bits). Additionally, as noted above, as the number of HARQ ACK/NAK bits increases relative to the number of CQI bits, the existing Rel-8 algorithms do not properly account for the weight of the HARQ ACK/NAK bits.